Phospholipids will be isolated from potassium transporting and non transporting Manduca sexta midguts. The phospholipids will be labeled with 32P, extracted with non polar solvents and separated by two dimensional thin layer chromatography. Both readioactivity and potassium concentration of the separated lipids will be measured and the turnover calculated. Our rationale is that phospholipids associated with the active transport process should turn over faster when the transport is taking place than when it is absent. Proteins and polypeptideionophores will be isolated using conventional techniques following a similar rationale. Changes in the ultrastructure of the midgut will be studied under three conditions: 1. while the postassium pump is decaying in the midgut isolated on a chamber 2. while the pump is turned on and off in isolated midguts and 3. while the pump is lost at the end of larval life. Proton transport will be studied by titramatic methods and a search for an inhibitor of the K transport will continue.